BACKGROUND The association of operative duration with the risk of venous thromboembolism (VTE) has not been quantified in neurosurgery. OBJECTIVE To investigate the association of surgical duration for several neurosurgical procedures and the incidence of VTE. METHODS We performed a retrospective cohort study involving patients who underwent neurosurgical procedures from 2005 to 2012 and were registered in the American College of Surgeons National Quality Improvement Project registry. In order to control for confounding, we used multivariable regression models, and propensity score conditioning. RESULTS During the study period, there were 94 747 patients, who underwent neurosurgical procedures, and met the inclusion criteria. Of these, 1358 (1.0%) developed VTE within 30 days postoperatively. Multivariable logistic regression demonstrated an association of longer operative duration with higher 30-day incidence of VTE (odds ratio [OR], 1.22; 95% confidence interval [CI], 1.19-1.25). Compared with procedures of moderate duration (third quintile, 40-60th percentile), patients undergoing the longest procedures (>80th percentile) had higher odds (OR, 3.15; 95% CI, 2.49-3.99) of developing VTE. The shortest procedures (<20th percentile) were associated with a decreased incidence of VTE (OR, 0.51; 95% CI, 0.27-0.76) in comparison to those of moderate duration. The same associations were present in propensity score-adjusted models, and models stratified by subgroups of cranial, spinal, peripheral nerve, and carotid procedures. CONCLUSIONS In a cohort of patients from a national prospective surgical registry, increased operative duration was associated with increased incidence of VTE for neurosurgical procedures. These results can be used by neurosurgeons to inform operative management, and to stratify patients with regard to VTE risk.